Content items, e.g., advertisements, can be identified by a search engine in response to a query. The query can include one or more search terms, and the search engine can identify and rank the content items based on, for example, the search terms, e.g., keywords, in the query and one or more parameters associated with the content item.
In some online advertising systems, advertisers pay for their advertisements on a cost-per-click basis. Advertisers can select the maximum cost-per-click the advertisers are willing to pay for each click of an advertisement. The cost-per-click charged for an identified advertisement can be calculated based on the other advertisements rated or positioned below the current advertisements and a click-through rate for the current advertisement in an auction process.
Determining an actual cost-per-click for the advertisements that is based on the other advertisements (e.g., ranked below the current advertisement) can result in an optimization of advertising revenue. Some advertising systems charge the maximum cost-per-click. However, other optimization processes can also be used to select a subset of advertisements to be displayed and the actual cost-per-click to be charged.